I. Field of the Invention
The present invention relates generally to an apparatus and method for performing computed tomography.
II. Description of Related Art
There are many situations where it is highly desirable to examine a component to determine if the internal structure of the component contains voids or other flawsas well as dimensional accuracy. In the automotive industry there are many components which, if these components contain a void or other flaw, would compromise the overall operation of the vehicle. For example, a void or other flaw in the engine block closely adjacent the combustion chamber may cause a complete failure of the engine during operation or otherwise compromise the safety and/or performance of the engine.
Such internal flaws of parts are not visible from the exterior of the part. In the automotive industry, internal portions of automotive parts have previously been visually inspected by destructive testing, where the part is physically cut into pieces. The destructive testing process has the disadvantage of destroying the sample, causing new defects during the cutting process and not allowing a large sample or all of the pieces to be inspected. Consequently, in order to examine these parts, there are previously known computed tomography (CT) machines. Such CT machines typically include an x-ray source and one or more x-ray detectors or x-ray film at a position spaced from the source. Each x-ray detector generates an output signal which varies in magnitude with the strength of the received signal from the radiation source.
The part to be examined is then positioned in between the radiation source and the radiation detector or detectors. The part is then scanned by rotating the part relative to the radiation source and the radiation detector thus performing a two-dimensional (2D) x-ray image of the part representative of the density of the part. Successive 2D imaging of the part at axially spaced positions along the part produces individual 2D slices which, when combined, produce a three-dimensional image of the interior structure of the part. In practice, a void within the interior of the part will create an increase in the detected radiation by the detector during the 2D imaging since voids necessarily absorb less radiation than the homogenous structure of the part.
The output from the detectors is then connected to a computer system which then generates an image of the internal structure of the part under examination. Any voids or other defects within the interior of the part are visible on the reconstructed image.
These previously known CT machines, however, all suffer from a number of common disadvantages. One disadvantage of the CT machine is that previously it has only been possible to scan a single part or component at a given time. Furthermore, a complete scan of the part takes an extended period of time which varies as a function of the number of 2D images performed.
Since a complete CT scan of a single part is time consuming, it is not practical to scan all of the production parts in a high part volume situation. Consequently, it has been the previous practice to simply select sample parts from the production run and to examine these parts using a CT machine. However, unexamined parts may contain serious voids or other flaws and yet go undetected.
A still further disadvantage of the previously known method for scanning individual parts with a CT machine is that the parts to be examined are typically shipped from the production facility and to the CT machine facility. At the CT machine facility, the parts are removed from their packaging and mounted on a fixture between the radiation source and detector of the CT machine. Following a complete scan of the part, the part is removed from the CT machine, reinserted into the shipping carton from the production facility, and shipped back to the production facility. All of these procedures, however, are necessarily labor intensive and thus expensive in labor cost.